Emergency medicine has emerged as a major specialty during recent years and involves initial management at the site of physiological failure or trauma, the transport to a formal medical facility and emergency room care. In connection with such emergency medicine, there has arisen a need to provide ventilatory care. Because of the complexities created by patients sized from a small infant to a large adult with their vast differences in pulmonary tidal volumes and the rates desired, it has been very difficult to provide a satisfactory ventilator which can meet these problems and at the same time be simple enough to operate so that it can be utilized by medical transport crews, paramedics and the like without unduly compromising the requirement of the patient being cared for. There is, therefore, a need for a ventilator which can meet these requirements.